A common logistical concern in businesses is the tracking of assets or persons. In retail, one example of this logistical tracking concern is shoplifting. Many retail establishments employ electronic tags attached to goods that can be detected by systems installed for that purpose. A common term for these systems, tags, etc. is electronic article surveillance, or EAS.
Many of these tags and systems are only capable of registering the presence of the tag. Transmitters and receivers are located at exit points within a retail environment and the transmitter creates an interrogation zone at the exits while the receivers scan for responses from tags passing through the interrogation zone. The transmitters and receivers are typically housed in pedestals. There are several types of tags for these systems, one of which is a harmonic tag and another of which is a resonance tag. With the harmonic tag, the electromagnetic interrogation field creates stored energy in the harmonic tag, and when the interrogation field is turned off this energy dissipates from the tag and produces a signal which is a harmonic of the interrogation field. The element that stores and dissipates the energy to generate the signal is typically comprised of a ferrite core with a wire coil around it, and it can be tuned to generate a signal at a particular frequencies. The system is tuned to the expected frequencies, and the receiver antennas of the system detect these signals. When a signal is detected within an interrogation field, it is assumed that a tag is present and that it is improperly being removed from the retail facility. Similar systems may also be used to identify authorized personnel at control points, etc.
There are many ways used to attach a tag to an article being protected. For clothing and similar items, a tag incorporating a tack is frequently used. The tack has a head and shaft extending from its head, while the tag body houses a clutch and has an aperture through which the tack shaft may be inserted into the clutch. Various clutches are employed in the art, and depending on the particular clutch, the clutch may be released by mechanical means, application of a magnet to the clutch, or some clutches may be released by multiple methods.
One clutch that is frequently used is a ball clutch. In a ball clutch, a spindle is located in the interior of a tapered cup which is opened at its larger end and has an aperture through its smaller, closed end. The spindle has a shaft through it which is aligned with the aperture of the tapered cup. Both the aperture in the tapered cup and the shaft through the spindle are at least large enough to accommodate the insertion of the tack shaft. The spindle has apertures through its walls which carry ball bearings that ride on the interior of the tapered cup. When the tack shaft is inserted the spindle moves to allow shaft in, but if the shaft is pulled, the ball bearings, the tack, and tapered cup wedge. The spindle must be retracted prior to pulling the tack in order for there to be space among the elements within the tapered cup to allow the removal of the tack shaft. In many ball clutches, the spindle is at least partially made of a magnetically attractable material, which allows it to be retracted by application of a magnet.
In many applications, it is desirable that the EAS tag be as small as possible. However, due to the shapes and sizes of the internal elements, the possible arrangements of the internal elements are limited. Some of these possible arrangements result in tag shapes which are vulnerable to tampering. For example, a tag with an elongated shape can provide sufficient purchase so that the tack and body portions can be gripped and twisted to separate the two portions. The embodiments of the current invention incorporate certain anti-twisting features to prevent tampering with a compactly configured EAS tag.